The Eugeneodontida is an extinct and poorly known order of cartilaginous fishes. They possessed "tooth-whorls" on the

symphysis A symphysis (, pl. symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing togethe ...

of either the lower or both jaws and pectoral fins supported by long radials. They probably lacked pelvic fins and anal fins. The palatoquadrate was either fused to the skull or reduced. Now determined to be within the

Holocephali Holocephali ("complete heads"), sometimes given the term Euchondrocephali, is a subclass of cartilaginous fish in the class Chondrichthyes. The earliest fossils are of teeth and come from the Devonian period. Little is known about these primit ...

, their closest living relatives are ratfish. The eugeneodonts are named after paleontologist Eugene S. Richardson, Jr. The Eugeneodontida disappeared in the

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a ...

. Members of the Eugeneodontida are further classified into different families, the most well-preserved members that have been discovered are commonly placed within the families

Helicoprionidae The Helicoprionidae, also known as the Agassizodontidae are an extinct, poorly known family of bizarre holocephalids within the poorly understood order Eugeneodontida. Members of the Helicoprionidae possessed a unique "tooth-whorl" on the symph ...

("spiral saws"), and Edestidae ("those which devour"), the former containing the genera ''

Helicoprion ''Helicoprion'' is an extinct genus of shark-like eugeneodont fish. Almost all fossil specimens are of spirally arranged clusters of the individuals' teeth, called "tooth whorls", which in life were embedded in the lower jaw. As with most exti ...

'', '' Sarcoprion'', and '' Parahelicoprion'', and the latter containing the genera '' Edestus'', '' Lestrodus'', and '' Metaxyacanthus''. All eugeneodonts are thought to have been obligate

carnivores A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

, with each genus having specialized feeding behaviors, territory ranges, and specific prey.

Taxonomy

*Superfamily Caseodontoidea **Family Caseodontidae ***Genus '' Caseodus'' ***Genus '' Erikodus'' ***Genus '' Fadenia'' ***Genus ''

Ornithoprion ''Ornithoprion'' is an extinct genus of eugeneodont holocephalan closely related to '' Caseodus.'' It lived in the Moscovian Moscovian may refer to: *An inhabitant of Moscow, the capital of Russia *Something of, from, or related to Moscow ...

'' ***Genus '' Pirodus'' ***Genus '' Romerodus'' **Family Eugeneodontidae ***Genus '' Bobbodus'' ***Genus '' Eugeneodus'' ***Genus '' Gilliodus'' **Family ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'' ***Genus ''

Campodus ''Campodus'' is an extinct genus of eugeneodont holocephalans from the Carboniferous. Likely one of the earliest and most basal caseodontoids, it can be characterized by its broad, ridge-ornamented crushing teeth made of various types of denti ...

'' ***Genus '' Chiastodus'' ***Genus '' Tiaraju'' *Superfamily Edestoidea **Family

***Genus ''

Agassizodus ''Agassizodus'' is an extinct genus of eugeneodont holocephalan from the Carboniferous. It belongs to the family Helicoprionidae, which is sometimes called Agassizodontidae. Like other members of its family, it possessed a symphyseal tooth who ...

'' ***Genus '' Arpagodus'' ***Genus '' Campyloprion'' ***Genus ''

'' ***Genus '' Parahelicoprion'' ***Genus '' Sarcoprion'' ***Genus '' Toxoprion'' **Family Edestidae ***Genus '' Edestus'' ***Genus '' Helicampodus'' ***Genus '' Lestrodus'' ***Genus '' Parahelicampodus'' ***Genus '' Syntomodus'' **Family ''

'' ***Genus '' Paredestus''

References

External links

Palaeos Vertebrates 70.100 Chondrichthyes: Eugnathostomata at paleos.com
JSTOR: Journal of Paleontology Vol. 70, No. 1 (Jan., 1996), pp. 162-165
at Devonian Times Eugeneodontida, Mississippian first appearances Mississippian taxonomic orders Pennsylvanian taxonomic orders Cisuralian taxonomic orders Guadalupian taxonomic orders Lopingian taxonomic orders Early Triassic taxonomic orders Early Triassic extinctions Prehistoric cartilaginous fish orders {{paleo-shark-stub